The Perfect Corner
The Perfect Corner
To the uneducated, racing must look pretty simple. Just drive really fast. Well, anyone who has done any competitive driving knows it is not quite so simple. Most drivers, however, get confused about the best line to take, and how to go about driving that line. When should I brake? What is the proper apex? When should I start getting on the throttle? Most racing classes and texts teach you about techniques such as late apexing and trail braking and so on, but they donít give you the tools to figure out exactly where and when you should be doing this. This article will give you a very simple system for working up each and every corner on the track. When I say simple, though, I certainly donít mean easy. After all, someone can explain how to hit a 95 mile per hour fast ball, but it would take years of practice to be able to do it consistently. This system, will however take away the confusion many drivers feel, and give you the confidence to know where you are making mistakes and give you a goal you can strive for.
Before I go any further, we should first understand what our goal is when it comes to driving the perfect corner. Simply put, it is to minimize the amount of time between periods of full throttle. Said another way, from the time you hit the brakes, you want to get back to full throttle as fast as possible. If you look at a data readout that shows lap times and average throttle position during the lap, almost as a rule they coincide. Higher average throttle position during a lap means lower lap times, simple as that.
Ok, so quit stalling, what is this magic technique?
- The first step is to find the apex point that if you pass it at maximum acceleration, you can just barely keep the vehicle on the course at track out.
- Get to this apex point as fast as possible.
Thatís it! Now go win some races.
Ok, maybe not quite yet, letís explain some of the nuances to this technique. Firstly, what do I mean by maximum acceleration? Basically as you cross the apex you should be giving the car as much throttle as possible while keeping the rear end under control. In a lower powered vehicle such as a Spec Racer Ford or 4-stroke kart this basically means full throttle in all but the slowest corners. In a high powered formula 1 car that can easily produce power oversteer in all but the fastest corners, you could be giving it almost no throttle at the apex and would not be at full throttle until almost track out. The key fundamental here is that if you are not at full throttle past the apex, it is not because you are going to run off the outside of the track, it is to keep the rear end from coming around.
Finding the Apex
Being at maximum acceleration at corner exit also allows us to pick the ideal apex point. If you find yourself running out of track, it means your apex was too early. If you are not pushed right to the edge of the track it means your apex was too late. This corner exit period also allows us to fine tune the balance of the car. Iíll delve more deeply into this in my next article Perfect Control, but basically your vehicleís balance should be determined by what allows you to get to full throttle as soon as possible.
As you get more familiar with your vehicle, you will notice that for any given speed there is a similar path you will take as you exit the corner. Imagine if you were in a parking lot and you took off as fast as you could, but also turning as hard as you could while keeping the rear end under control. The radius of your turn would open up pretty quickly at the start as you gained speed quickly, then the radius would taper off until you were driving in a circle as friction matched engine power and you could accelerate no more. You can imagine how cars of different acceleration potential would follow a different path with higher powered cars opening up their radius faster. This is the essence of why your apex is later with higher powered cars and tighter corners, because the radius of your acceleration arc opens up faster.
More about the Apex
I wanted to talk a little bit more about the apex. It is not simply a point on the track, but it also relates to which direction the vehicle is going. To illustrate this think of a cone on an autocross course that is setup as a hairpin turn. You have to drive down around the cone and come back as fast as possible. We have to pick a point that we begin accelerating. Every point around the cone is in virtually the same place, so what is more important is the direction your car is going, not the point you are at on the cone as the difference in this case would be mere inches.
This single cone example is similar to what the apex of tighter corners will be like on the track. In these cases you should pay more attention to the direction your vehicle is heading to give you cues to when to accelerate rather than to a certain point you are at. At the opposite end of the spectrum, think of a very long fast corner on a narrow track, it is much harder to tell which direction your car is heading in relation to the corner and you should be paying more attention to finding a specific point on the track that allows a proper corner exit.
So now that we have established our ideal apex, our second job is to get there as soon as possible. So how do we do that? In short, trailbrake as much as possible. This means using the brakes as hard and as late as possible as you aim down for your apex. In fact you only want to get off the brakes just in time to get your foot over to the gas and start feeding in throttle so you are at your maximum acceleration as you pass the apex. As a practical matter this generally means there is still time in the corner where you are essentially coasting, between brakes and hard acceleration. Depending on how stiffly sprung a vehicle is, there is a certain amount of time you must wait for the load to transfer, but your goal is to minimize this time. This is one advantage of left foot braking as it allows a smoother and faster transition from brakes to throttle.
When I say as hard as possible though, I donít mean you are giving full brakes all the way down to the apex. This is for two reason, first because there is often grass and sand in the way if you tried to drive straight to the apex and second because there is still a certain amount of direction change that has to be accomplished before you hit the apex. If you are giving full brakes, you have no grip left over to turn.
So whatís the answer? You want to try and spread the direction change out as much as possible. This means turning in as early as you can without hitting the inside of the track before the apex. You will ideally be letting off the brakes smoothly as you turn more and more into the corner so you finally let off the last little bit of brakes just as you approach the apex. This technique will smoothly decrease the radius of your arc down to the apex. The classic alternative is what many schools and texts teach. Turning in later and letting off the brakes quicker and then maintaining a fairly constant arc (or actually accelerating and opening up your arc) before the apex. This is actually still trailbraking although only the small amount as you turn in. The reason more trailbraking is faster is because you will still arrive at the apex at the same speed as the classical technique but if you are decelerating more as you get there you have carried a higher average speed up to that point. Higher average speed equals lower times. More trailbraking also dictates that you are traveling a straighter and shorter path which again equals lower times. Also, in a competitive driving situation this makes you harder to pass because as an added benefit you are closer to the inside edge of the track and there is less room for other vehicles to get by.
If youíve paid attention up to this point, youíll realize where your throttle application point is, and that is really the key to what makes this whole technique work. Your throttle application point should be right before the apex giving you just enough time to shift the load to the rear and prepare the vehicle for maximum acceleration. This is basically a hard rule and the only times you deviate are multiple event corners such as compromise corners and double apexes. In these cases you must get on the throttle sooner, because the geometry of the corner does not allow you to brake all the way down to the final apex, although in general your goal is still to make your throttle application point as late as possible.
But wait, I hear you say, Iíve always heard you are supposed to get on the gas as soon as possible? That is true, but the trick is that this should be based on time not distance. Just google late apex and you can find many illustrations depicting a tight arc at corner entry and then an unwinding of the steering while feeding in the gas before the apex. This is almost considered common knowledge, the only problem is that it is wrong. In order to do this tight arc at the beginning of the corner you would have to slow down more than had you done a gentler arc down to the apex, plus you have traveled a greater distance, and since you are going slower when you start accelerating you canít give it as much throttle. So although you got on the gas earlier in distance in the corner, you could have gotten back to full throttle faster in time, and after all time is what matters in racing.
The interesting thing about this is that in both cases your corner exit speed is normally, virtually the same. In the early acceleration scenario you are accelerating longer, but starting from a slower speed. By the time you make it to corner exit, you generally end up equaling the speed you would have achieved had you started accelerating at the apex, but starting from a higher speed. In the early acceleration scenario; however, the corner entry section took longer to complete because you were going slower through this part and taking a longer path. This often explains the differences you see between good and great drivers. Most all proficient drivers will have about the same corner exit speed, but if you look at the corner entry speeds of the greats, it is usually higher, and what makes the difference in lap times.
Before we move one I also wanted to point out that you can also use the throttle application point to determine your braking point. First off, and more obvious, if you go wide and canít make it down to the apex it means your braking point is too late. But, if you feel like you can get on the throttle much before the apex it means you can move your braking point up some. Actually it could also mean you might benefit from double apexing the corner, but weíll get to that in a future article.
I should also mention corners in which you donít use the brakes, but only need to lift the throttle some. In this case you still want to try and carry as much throttle as possible deep into the corner and do what ever lifting you have to do closer to the apex.
Again, if you are getting on the throttle much before the apex, your corner entry is slower than it could have been, and you can brake deeper.
So now letís walk, er drive, through a typical corner so we can reiterate the things we should be looking for.
Accelerating down the straight to we brake hard and fast at the 2 marker right before a tight 180 degree hairpin. We start to slowly let off the brakes to give the front tires enough traction to turn in toward our apex which is just past the central point of the corner. We try and turn in as early as possible, straightening out the corner entry. We know that if we turn in too much too soon, though, weíll run into the inside of the turn too quickly and have to unwind the steering and lose time. Weíve carried as much speed deep into the turn as we could trailing the brakes the whole way and arrive right at the midpoint of the inside curbing just as we smoothly release the last bit of pressure from the brakes. Immediately we shift our foot to the throttle and start to feed it in as aggressively as we can but smoothly enough to allow the load to transfer to the rear to give the rear tires more traction. Just as we pass the apex we feel the rear end start to move out just bit, and we know weíre right on the edge of traction. The steering gets lighter as load shifts to the back, but we can still feel the front tires biting and know our balance feels right. We feed in the throttle smoothly and now our foot is flat to the floor. We can see the edge of the track coming up quickly, too quickly. Our ever widening arc is carrying us off the track and weíre going to have to lift just a little so we donít run off. Oh well, we lost a little bit of time there, weíll remember next time to apex a little later.
Hopefully this little exercise helped you visualize the kinds of cues you should be looking for while trying to work up to the perfect corner.
Of course there are exceptions to any rule and generally these deal with either a unique feature of the vehicle or the track. Here are some examples:
Because of the basic design of karts, there are certain compromises you will have to make at corner entry. First off, in the case of a kart with only rear brakes, you will not be able to trail the brakes as hard as if you had front brakes. In this case the harder you try and use the brakes the more load transfers to the front and the less effective your brakes are. The solution is to drive the more traditional wider corner entry arc and use the tire scrub to slow you down as you approach the apex. You will have a slower than ideal corner entry, but if you try and turn in earlier and use more brakes, you wonít be using very much of the front tireís traction to slow you down, and that would make you even slower still. This does not change the apex finding and throttle application techniques described above, but it will compromise your corner entry.
Secondly, I have heard from people in karts that have front-brakes that have problems trail-braking. Again the issue, as it usually is with karts, is keeping the rear inside tire jacked. Proper trail-braking in a kart therefore, becomes very setup dependent and is not as easy as it is in cars that have a differential. The primary issue is that a certain amount of jacking is caused by chassis flex caused by the load of the driver in the seat through the seat struts. During a braking and turning maneuver, the driver braces himself more against the pedals and steering and the seat is not taking much of the load. This not only stiffens up the chassis, but causes more of the load to be transmitted directly to the front of the kart ahead of the softer waist area. The end result is less chassis flex, and therefore less jacking, and if your kart was just barely unloading the inside rear enough you will now have significantly increased understeer. On the flip-side however, the direction of g-forces acting on the CG are going in a more favorable direction to promote jacking through front-end geometry. So possibly looking more to caster/track changes to increase jacking could help you.
Either way, if you find this happening to you, you can try and increase the amount of jacking either through chassis flex or front end geometry changes. Look to the setup section of this site for more information about this. You can also try more of a wraparound seat that will take more of the load in a forward direction and not just sideways as in standard kart seats. Driving technique also plays a role in allowing your kart to jack during trail-braking. If you are new to trail-braking you may not be generating the kinds of forces at the tires required to flex the chassis enough. In the end, as it usually is in racing, you may be looking at a compromise of some kind. You may have to have a later and faster turn-in than what is ideal in order to get your kart to jack properly at corner entry. There will be time lost, but you can still make the most use out of your current machine by striving to brake as far down to the apex as your kart allows. Even if your corner entry is compromised however, that is the least important part of the corner time wise and you can still focus on the apex finding and throttle application techniques described above to try and improve your times.
Changing Traction Levels
What if there is a bunch of sand sitting on the track right at corner exit? Or a part of the corner that is more banked than others? Obviously we have to take this on a case by case basis, but the general rules still apply. Often the main thing this will change will be your line. As an example, letís say you do have sand sitting at corner exit. The main goal at corner exit is to be at full throttle. If the sand is so slick that it induces wheelspin you might try apexing a little later and driving over the sandy part straighter, but still going right to the edge of the track. The main point is to try and deal with the problem by altering your line and steering, not by lifting. As another example, what about rain driving? On a well worn track the line is like ice as you cross over it, so you want to avoid practically every part you normally would drive on. In this case you have to go find the grip, but the general rule of minimizing time between full throttle still exists. The main difference is the geometry of the track has essentially been altered, and you have to find a new apex that is often several feet from the real one. I could probably think of countless other examples, and you have to look at each one as a problem to be solved, but hopefully you can use the basic guidelines of the perfect corner technique to figure it out.
So to wrap up, letís review by listing out the fundamentals of The Perfect Corner
- Use the brakes as much as possible during the turn down to the apex with the goal of only getting off of them just in time to allow you to transition to throttle before the apex.
- If you go wide and canít make it down to your apex your braking point is too late.
- If you donít need to brake all the way down to the apex your braking point is too early (or you might benefit from double apexing).
- Get on the throttle as hard as possible right as you pass the apex. If you feel you can get on the gas sooner than this, your braking point is too early.
- The only reason you should not be at full throttle during corner exit is to keep the rear end from coming around, not because you are going to run off the track.
- If you run wide at exit you need a later apex.
- If it is easy to keep the vehicle on the track at corner exit you need an earlier apex.
Remember this technique only deals with single corners and not multiple event ones such as double apexes and chicanes. That will be the subject of a future article.
Next up in the series Perfect Control will deal with using your vehicle to itís maximum potential as you learn to develop perfect control at the limit.